1. Field of the Invention
This invention relates to radio-frequency identification readers used in conjunction with identification tags in controlled access systems, and more particularly is directed to low power proximity readers suitable for battery powered operation.
2. State of the Prior Art
Radio Frequency Identification Systems (RFID) have come into widespread usage and generally include a reader, typically installed in a fixed location, and a population of portable identification tags. Each ID tag contains a transponder unit which returns a coded response when interrogated by a radio-frequency transmission from the reader. The reader periodically sends out a transmission designed to evoke a radio-frequency response from any ID tags within range of the reader. The tag response includes coded identification data based on which the reader makes a decision to grant or deny access to controlled facilities. RFID systems may use active tags which carry their own source of power such as a battery, or passive tags which contain no source of power and instead rely entirely on energy radiated by the reader unit. Passive tag readers continually or periodically search for the presence of passive tags in the vicinity of the reader by transmitting energy which will activate any tag present. A passive tag does not announce is presence unless activated by the reader. Furthermore, the passive ID tag requires that is receive sufficient radio-frequency power which, when converted by the tag into the electrical current, will support operation of the tag's electronic circuits. Consequently, the operating range of the reader/tag system is to a large extent determined by the power transmitted by the reader, and the ID tag must come into sufficient proximity to the reader for the tag to be activated. For this reason passive tag readers as also known as proximity readers. Proximity readers typically have substantially greater operating power requirements than active tag RFID readers of comparable range, and the development of portable battery powered proximity readers has been hindered by excessive power drain on the batteries.
A continuing need exists for RFID readers of reduced operating power requirements and, in particular, for a low power proximity reader which can be adequately powered by batteries for portable use.